The Internet, like so many other high tech developments, grew from research originally performed by the United States Department of Defense. In the 1960s, the military had accumulated a large collection of incompatible computer networks. Computers on these different networks could not communicate with other computers across their network boundaries.
In the 1960s, the Defense Department wanted to develop a communication system that would permit communication between these different computer networks. Recognizing that a single, centralized communication system would be vulnerable to attacks or sabotage, the Defense Department required that the communication system be decentralized with no critical services concentrated in vulnerable failure points. In order to achieve this goal, the Defense Department established a decentralized standard communication protocol for communication between their computer networks.
A few years later, the National Science Foundation (NSF) wanted to facilitate communication between incompatible network computers at various research institutions across the country. The NSF adopted the Defense Department's protocol for communication, and this combination of research computer networks would eventually evolve into the Internet.
Internet Protocols
The Defense Department's communication protocol governing data transmission between different networks was called the Internet Protocol (IP) standard. The IP standard has been widely adopted for the transmission of discrete information packets across network boundaries. In fact, the IP standard is the standard protocol governing communications between computers and networks on the Internet.
The IP standard identifies the types of services to be provided to users and specifies the mechanisms needed to support these services. The IP standard also specifies the upper and lower system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in the system.
In a typical Internet-based communication scenario, data is transmitted from an originating communication device on a first network across a transmission medium to a destination communication device on a second network. After receipt at the second network, the packet is routed through the network to a destination communication device using standard addressing and routing protocols. Because of the standard protocols in Internet communications, the IP protocol on the destination communication device decodes the transmitted information into the original information transmitted by the originating device.
The IP-Based Mobility System
The Internet protocols were originally developed with an assumption that Internet users would be connected to a single, fixed network. With the advent of cellular wireless communication systems using mobile communication devices, the movement of Internet users within a network and across network boundaries has become common. Because of this highly mobile Internet usage, the implicit design assumption of the Internet protocols (e.g. a fixed user location) is violated by the mobility of the user.
In an IP-based mobile communication system, the mobile communication device (e.g. cellular phone, pager, computer, etc.) can be called a mobile node or mobile station. Typically, a mobile station maintains connectivity to its home network while operating on a visited network. The mobile station will always be associated with its home network for IP addressing purposes and will have information routed to it by routers located on the home and visited networks.
Packet-Based Communication Systems
In Internet Protocol (IP) networks, the communication process is very different from prior conventional telecommunication systems. In an IP network communication, there is no open switched connection established between the caller and recipient devices. The information being transmitted between the caller and recipient devices is broken into packets of data, and each packet of data is transmitted to the recipient device in pieces. The data packets individually contain routing information to direct each packet to the recipient device. These packets are then reassembled into a coherent stream of data at the recipient device.
The Internet protocols were originally developed with an assumption that Internet users would be connected to a single, fixed network. With the advent of cellular wireless communication systems using mobile communication devices, the movement of Internet users within a network and across network boundaries has become common. Because of this highly mobile Internet usage, the implicit design assumption of the Internet protocols (e.g. a fixed user location) is violated by the mobility of the user.
In an IP-based mobile communication system, the mobile communication device (e.g. cellular phone, pager, computer, etc.) can be called a Mobile Node. Typically, a Mobile Node maintains connectivity to its home network through a foreign network. The Mobile Node will always be associated with its home network for IP addressing purposes and will have information routed to it by routers located on the home and foreign networks. The routers can be referred to by a number of names including Home Agent, Home Mobility Manager, Home Location Register, Foreign Agent, Serving Mobility Manager, Visited Location Register, and Visiting Serving Entity.
Cellular Communication Systems
A typical cellular communication system is comprised of multiple cell sites, each covering an intended geographic region. Each of the cell sites can be assigned an address for routing information packets, and each of the Mobile Nodes can be assigned an address for their physical connectivity to the cell site.
Each cell site supports voice and data communication to the linked Mobile Nodes present within that geographic area. A wireless communication link is maintained by a transceiver at or very near the center of the cellular coverage area. The transceiver is coupled to a base station transceiver substation which is coupled to a base station controller, with controls the packet transmissions within the cell site area. The base station controller is also coupled to a mobile switching center, which routes calls handled by the base station controller and base transceiver station to a public switched telephone network or a packet data service node interface with the Internet.
Information packets on the communication system are processed by the base station controller for transmission to the public switched telephone network or the Internet. The base station controller processes the information packets for transmission to the public switched telephone network, the Internet, or the Mobile Node. As a Mobile Node moves across cellular boundaries, it changes its connectivity and its connectivity address. Routers on the communication network have to be updated with this new connectivity address so that information packet can continue to be properly routed. The address used for routing can be a single IP address, a combination of an IP address and a connectivity address, or some other similar addressing scheme providing packet routing data on the communication network corresponding to the physical connectivity of the Mobile Node.
Telecommunication networks are complex networks used to establish connections between two or more telecommunication devices. Frequently, the devices involved with a telecommunications call or connection are referred to as the originating device and the terminating device. The user typically enters an identifying number into the originating device of the terminating device to which a call is to be placed. The network responds to entry of the identifying number of the terminating device and performs a call setup procedure that establishes, among other things, a connection between the originating device and the terminating device using IP addressing. Call data, voice or multimedia, is then routed between the two devices according the IP addressing assigned to each device.
Voice and data transmitted according to the IP packet standard is the evolving and most current communication protocol for cellular telephone communication. With this migration to the IP standard and miniaturization of computer chip technology with dramatic increases in clock speeds, computational power, and memory storage has come increasingly sophisticated services such as email access, streaming video and audio data transfers, instant messaging, text messaging, multimedia applications, picture messaging, Internet website access, e-commerce applications, games and other services. Cell phones have accordingly evolved from relatively crude devices limited to telephony communication to near mini-computers with operating features and capabilities equal to if not superior to early personal computers.
Code Division Multiple Access (CDMA) is an evolving third generation communication system standard for wireless communication systems that can transmit multimedia services using the packet-based Internet protocol. These CDMA mobile communication systems support multimedia telecommunication services delivering voice (VoIP) and data, to include pictures, audio, video, streaming video, messaging, and other multimedia information over mobile wireless connections.
As the capability of the various communication standards have improved, there has been an increasing need for high-speed transmissions and increased user capacity. A new CDMA packet air interface has been developed that offers improvements over earlier CDMA systems by implementing high-speed shared-traffic packet data channels on the forward air-link connection. Recent developments include CDMA-based 1xEV systems operating at 1.25 MHz. The 1.25 MHz carrier delivers high data rates and increased voice capacity. 1xEV is a two-phase strategy. One phase is designated 1xEV-DO, which handles data only. The 1xEV-DO standard provides user with peak data rates of 2.4 Mbits/s. The other phase is 1xEV-DV, for data and voice. Other standards are evolving that also make use of the shared packet channel and multiplex packet communication for high-speed data and voice communication.
On the CDMA standard, Mobile Nodes, or Access Terminal (AT), roam within and across cellular communication sites. Each of the cells possesses one or more transceivers coupled to a Base Transceiver Station (BTS) onto the communication network. The BTSs are in turn coupled to an Access Network. As an AT migrates across cellular borders, its BTS physical connection changes. An AT can be physically located anywhere on the network or sub-network, and its routing address data will change and require updating on other nodes. Wireless IP networks handle the mobile nature of AT with hand-off procedures designed to update the communication network and sub-network with the location of the mobile node for packet routing purposes. Because mobile nodes can move within sub-networks and between networks, hand-off procedures are needed to insure that packets are continually routed to the recipient AT as it moves from one network to another or from one sub-network to another.
As the CDMA standard evolves, newer methods and enhancements to transmitting packets on the network are being developed and deployed. There is a currently a need for a hand-off method compliant with the Interoperability Specification (e.g. TIA 856A and TIA 1054), which defines a standardized protocol interface between the base station and packet-switching equipment (PDSN, PCF). This will provide a standardized method for performing hand-offs.